Apparatus for making heat exchanger tube

ABSTRACT

Heat exchanger tube wherein the outside and/or inside surfaces of the tube have a heat exchange enhancement pattern formed in them. The heat exchange enhancement pattern does not extend through the full wall thickness. It is possible for the heat exchange enhancement pattern to include longitudinally extending variations in the type of enhancement. A process and apparatus for forming the tube provide for patterning metal strip and then forming the strip into the shape of a tube and then joining the longitudinally extending edges of the strip to form the complete tube.

United States Patent [191 McLain 1 1 APPARATUS FOR MAKING HEAT EXCHANGER TUBE [75] Inventor: Charles D. McLain, Alton, 111.

[73] Assignee: Olin Corporation, New Haven,

Conn.

[22] Filed: June 18, 1973 [21] App]. No.: 371,133

Related U.S. Application Data [62] Division of Ser. No. 214,034, Dec. 30, 1971.

[52] U.S. Cl 228/17, 29/33 D, 72/52,

219/8.5, 219/59 [51] Int. Cl 823k 1/20 [58] Field of Search 228/15, 17; 219/8.5, 59;

1 1 Jan. 7, 1975 2,600,254 6/1952 Lysokey 72/198 X 3,172,194 3/1965 Pauls 72/198 X 3,337,944 8/1967 Morris 219/59 X 3,406,271 10/1968 Cachat et a1 219/85 Primary Examiner-Francis S. Husar Assistant Examiner-Robert J. Craig I Attorney, Agent, or FirmR0bert H. Bachman [57] ABSTRACT Heat exchanger tube wherein the outside and/or inside surfaces of the tube have a heat exchange enhancement pattern formed in them. The heat exchange enhancement pattern does not extend through the full wall thickness. It is possible for the heat exchange enhancement pattern to include longitudinally extending variations in the type of enhancement. A process and apparatus for forming the tube provide for patterning metal strip and then forming the strip into the shape of a tube and then joining the longitudinally extending edges of the strip to form the complete tube.

8 Claims, 14 Drawing Figures TUBE FORM/N6 5 TRIP G 5 SUPPLY PATENTED 3,858,785

sum 1 or 4 PATENTED 3.858.785

sum sur 4 STRIP srp/p TUBE WELDING SHAPING SUPPLY FPATTERN/NG', FORM/N6 OR M/LL STAT/ON SIZING MILL FURTHER PROCESSING PATENTED 3858,78?)

S TRIP F il l vG SUPPLY ML L APPARATUS FOR MAKING HEAT EXCHANGER TUBE This is a division, of application Ser. No. 214,034 filed Dec. 30, 1971.

SUMMARY OF THE INVENTION BACKGROUND OF THE INVENTION This invention deals with a process and apparatus for forming heat exchanger tubing having an enhanced surface for improved heat exchange efficiency. Enhanced surface heat exchanger tubing is also part of the instant invention. Preferably, the tubing in accordance with this invention is made by a process of welding metal strip having an enchanced surface into tubing as, for example by the use of high frequency welding.

It is known in the art to weld metal strip into tubing by high frequency welding. A typical example of a prior art apparatus and process is set out in U.S. Pat. No. 3,037,105, granted May 29, 1962.

In accordance with this invention, a process has been developed wherein strip is patterned on at least one of its major faces in such a manner as to improve its heat transfer properties when employed in a heat exchanger environment.

The patterned strip is formed into a tube and the strip edges are welded together. Preferably, the welding is done by the forge welding technique and set out in U.S. Pat. No. 3,037,105. By this process, it is possible to obtain heat exchanger tubing having enhanced heat exchange surfaces of a unique nature.

Since the enhanced heat exchange surface is formed by patterning metal strip, it is possible to obtain heat exchanger tubing having enhancement patterns which vary in degree of enhancement or which vary from one enhancement pattern to another. These variations preferably occur in the longitudinal direction as will be illustrated herein.

In accordance with this invention, the enhancement patterns on the inside and/or outside of the tube do not extend throughout the thickness of the tube wall. Therefore, it is possible to have different enhancement patterns on the inside and outside of the tube. The types of patterns which can be formed are unlimited since the enhancement is done on strip which is then formed up and welded into tube. Therefore, it is possible to form patterns such as a knurled diamond pattern on the inside surface of a tube which could not otherwise be formed.

In accordance with this invention, it is possible to form tubing where in the enhancement patterns on the inside and outside surfaces are selected to provide maximum efficiency for the different heat exchange functions which the inside and outside surfaces provide. For example, the tube might have a diamond pattern on its inside surface which provides a highly efficient nucleate boiling surface which is highly effective for evaporation purposes and a longitudinally extending rib pattern on its outer surface which is highly effective for condensing applications.

Other combinations are possible such as a diamond pattern on the inside or outside surface of the tube which is enhanced to a lesser degree along the longitudinal direction of the tube. This would provide an improved condensing surface since most of the condensation occurs at the beginning of the tube. The enhancement to a lesser degree in the latter portion of the tube would reduce drag and therefore increase efficiency.

In such a tube, it is possible that the other surface of the tube may be either unpatterned or patterned as desired. It is further possible in accordance with this invention that both the inside and outside surfaces of the tube may have the same enhancement pattern.

The patterned strip for welding into tubing in accordance with this invention may be formed off line or in line with the welding apparatus. When the patterning operation is performed in line, several advantages are provided in that one may change from one pattern to another or change the degree of enhancement more readily.

While high frequency welding is preferred in accordance with this invention, other well known joining processes could be employed. High frequency forge welding, however, provides a marked improvement by virtue of its extremely narrow weld zone.

The apparatus in accordance with this invention is directed to the in line patterning approach and comprises a strip patterning means located in line with the tube forming means and joining means. The strip patterning means preferably comprises embossing rolls. To obtain the aforenoted variations in enhancement patterns, it may comprise a plurality of embossing roll stands.

It is accordingly an object of this invention to provide a process and apparatus for forming a heat exchange enhancement pattern on metal strip which is then formed into welded tubing.

It is another object of this invention to provide a process and apparatus as above which enables the enhancement pattern on the strip to be varied in either degree of enhancement or from one pattern to another.

It is another object of this invention to provide heat exchanger tubing having a surface with an enhancement pattern which varies in degree or type of pattern along the length of the tube.

It is a further object of this invention to provide a heat exchanger tube having an enhancement pattern on its inside and/or outside surfaces.

It is a still further object of this invention to provide a heat exchanger tube as above, wherein the enhancement pattern on the outside surface of the tube is different from the enhancement pattern on the inside surface of the tube.

Other objects and advantages will become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A, 1B and 1C show a series of perspective views illustrating exemplary heat exhanger tubing in accordance with this invention.

FIGS. 2A, 2B, 2C, 2D, 2E and 2F show a series of perspective views illustrating other embodiments of heat exchanger tubing in accordance with this invention.

FIG. 3 is a schematic representation of an apparatus in accordance with this invention.

FIGS. 4A and 4B show a series of perspective views illustrating roll embossment of the enhancement pattern in the metal strip.

FIG. 5 is a cross section of the welded tube at the point of welding for a tube having a ribbed outer surface.

DETAILED DESCRIPTION OF TI-IE PREFERRE EMBODIMENTS Referring now to the drawings and especially to FIG. 1, there is shown a plurality of tubes 1 in accordance with this invention having heat exchange'e'nhancement patterns E on their inside 4 and/or outside surfaces. All of the tubes 1 have in common a longitudinally extending weld seam 6 since they are formed from metal strip which has been patterned and then welded into tubing.

FIG. 1A shows a tube having a diamond type pattern 2 which is better described .as a flat face diamond knurled type pattern on its outside 5 surface. The pattern 2 may be formed in any desirable manner; however, it is preferred, as will be shown herein, to form the pattern by roll embossing.

FIG. 1B shows a tube having a diamond type pattern 2 onthe outside surface 5 and a longitudinally extending rib type pattern 3 on the inside surface 4.

FIG. 1C shows a tube having a diamond type pattern 2 on the inside surface 4 and a longitudinally extending rib type'pattern 3 on the outside surface 5.

Therefore, it can be seen that in accordance with one embodiment of this invention that tubing 1 is formed by welding so that it has a longitudinally extending weld seam 6 with aheat exchange enhancement pattern E on its inside 4 and/or outside 5 surfaces. The enhancement pattern B may be the same on both the inside 4 and outside 5 surfaces or the enhancement pattern E may be different one from the other.

Referring again to FIG. 1A, the diamond pattern 2 shown therein comprises diamondshaped areas 7 having a flat face 8 separated by grooves 9. The pattern is relatively easy to form using conventional knurling rolls; however, the kn'urling operation is not carried out to the full depth of the pattern in the knurling rolls in order to form the flat faced diamond as shown.

' The surface shown in'a'highly efficient heat transfer surface. The formation of this type of surface on the inside of a tube would be virtually impossible except by the use of a method which welds patterned strip into tubing.

It should be evident from the tubes 1 shown in FIG. 1 that the depth of the heat exchange enhancement pattern E in the tube surfaces 4 and 5 is substantially less than the thickness of the tubes walls, thus making it possible for the enhancement pattern E on the inside surface 4 of the tube to be-different from the enhancement pattern E on the outside surface 5 of the tube.

The longitudinally extending rib type pattern 3 shown in FIGS. 18 and 1C is a highly effective heat transfer surface somewhat analogous to the heat transfer surface of U.S. Pat. No. 3,291,704, granted Dec. 13, 1966.

Therefore, it is possible in accordance with this invention to provide tubing for applications such as in US. Pat. No. 3,244,601, granted Apr. 5, 1966, wherein the inside and outside surface of the tube serve different heat exchange functions. For example, condensation takes place on one surface whereas evaporation takes place on the other. In accordance with the patent,

- the heat exchange surface is identical on both sides of the tube. In accordance with this invention, however,

the enhancement patterns Eon the heat exchange surfaces on the inside 4 and outside 5 of the tube 1 may be selected as desired .for a specific heat exchange function such as condensation or evaporation, so as to provide-optimum heat transfer qualities.

For example, it has been found that while the diamond type enhancement pattern 2'can be used for both evaporation or condensation, it is most effective whenused for evaporation. Similarly,'it has been found that the longitudinally extending rib type pattern 3 is most effective for condensation.

Therefore, the tube 1 of FIG. 18 would be uniquely suited for use in an apparatus where the outside surface 5 provides evaporation and the inside surface 4 provides condensation. The tube 1 of FIG. 1C would be uniquely suited for a similar apparatus where the functions of the respective surfaces 4 and 5 are reversed.

To produce the tubing of FIG. 1 by means other than the welding of patterned strip into tubing would be expensive and difficult and in some cases impossible. The particular enhancement patterns 2 and 3 shown in FIG. 1 are those which are preferred in accordance with this invention, however, the invention is notlimited to them. Any heat exchange enhancement pattern E which can be formed in metal strip which is later to be welded into tubing could be employed.

FIG. 2 shows a series of perspective views illustrating other embodiments of heat exchange tubingl'. In accordance with these embodiments 1, the heat exchange enhancement pattern E is varied over the inside 4 or outside 5 or both surfaces of the tube.

Because the tubing in accordance with this invention is formed from patterned strip, any desired pattern can be employed. Therefore, it is possible to vary the pattern on a given surface'4 or 5 of the strip. The pattern E may vary over the width of the strip or longitudinally along the strip or both. This will produce tubing I having a heat exchange enhancement pattern E varying about the circumference of the tube inside or outside or varying along the longitudinal length of the tube or a combination of these variations. g

It is preferred, however, in accordance with this invention, for purposes of heat exchange applications that the variations in heat exchange enhancement patterns E take place longitudinally along the tube 1'. The variations in enhancement pattern E generally fall into two preferred groups. In the first grouping, as shown in FIGS. 2A and 2D, there is a variation in degree or intensity of enhancement. By this it is meant that the depth of the enhancement pattern E is gradually decreased or the sharpness of the enhancement pattern E is gradually decreased or the enhancement pattern E is otherwise changed so as to gradually fade into a smooth surface.

Such an enhancement pattern E is shown on the inside surface 4 of the tube 1' of FIG. 2A wherein a diamond pattern 2' is employed with the depth of the grooves 9 separating the flat diamond faces 8 gradually decreasing along the length of the tube until the diamond pattern at the far end 10 of the tube is almost obliterated. Such a pattern 2' is uniquely suited in applications where most of the heat exchange occurs at heat transfer efficiency at the upstream end 11 where most of the heat exchange is occurring and gradually changes over the length of the tube until the enhancement pattern E is virtually obliterated thereby providing less drag on the heat exchange fluid and, therefore, the overall tube is improved in heat exchange efficiency.

The outside surface 5 of the tube 1' of FIG. 2A has a longitudinally extending rib pattern 3; however, it could have any desired enhancement pattern E or any which will be described hereinafter or it could be left smooth as in FIGS. 28 and 2C.

FIG. 2D shows a similar enhancement pattern 2' as in FIG. 2A though it is on the outside tube surface 5 and the inside tube surface 4 has been left smooth.

The second general grouping of variations in enhancement patterns is illustrated in FIGS. 28, 2C, 2E and 2F comprising tubes wherein the enhancement pattern E is changed from one pattern to another or from an enhancement pattern E to an unenhanced surface along the longitudinal length of the. tubing 1.

FIG. 2B shows just such a tube 1. In FIG. 2B, the internal surface 4 has a diamond pattern 2 extending longitudinally from the upstream portion of the tube 1' up to line 21 and the remaining portion 22 of the tube 1 has a smooth unenhanced internal heat exchange surface.

As with the tubing of FIG. 2A, the tubing 1' of FIG. 2B provides maximum heat exchange efficiency at the upstream portion 20 of the tube where the greatest amount of heat exchange is to occur while in the downstream portion 22 of the tube, enhancement has been eliminated so as to reduce drag on the heat exchange fluid which should thereby increase the overall efficiency of the heat exchanger tube. The outside surface of the tube 1' in this case has been left smooth and unenhanced; however, it may have any desired enhancement pattern E in accordance with this invention.

In FIG. 2C yet another variation is shown wherein the upstream portion 24 of the tube 1' has a diamond pattern 2 and the downstream portion 25 of the tube has a longitudinally extending rib pattern 3. In this tube 1', the diamond patterned portion 24 could provide maximum heat exchange efficiency for a desired heat exchange function as, for example, evaporation and the longitudinally extending rib portion 25 could provide improved heat exchange efficiency with reduced drag on the heat exchange fluid. While the rib portion 25 may not be as efficient for this heat exchange function as compared to the diamond portion 24, the reduction of drag in the rib portion 25 of the tube should improve the overall heat exchange efficiency of the tube.

FIGS. 2E and 2F show the heat exchange enhancement patterns E in the outside surfaces 5 of the tubes 1' corresponding to the heat exchange enhancement patterns of FIGS. 23 and 2C which were on the inside surfaces 4. The enhancement pattern E or lack of it in FIGS. 2E and 2F on the inside surface may be chosen as desired.

It is also evident from a consideration of FIG. 2 that the variationin enhancement pattern E may be present in both the inside 4 and outside 5 surfaces of the tube 1' and the type of variation whether of the grouping of FIGS. 2A and 2D or the grouping of FIGS. 28, 2C, 2E and 2F may be varied as between the inside 4 and outside 5 surfaces of the tube 1'.

could be readily thought of from a consideration of FIGS. 1 and 2 and the specific combinations shown therein are not meant to be limitive of the invention though they do represent the preferred embodiments in accordance with this invention.

The process in accordance with this invention comprises providing a flat metal strip which is then patterned to form a heat exchange enhancement pattern in one or both of its major faces. The particular patterns which may be formed may be chosen as desired to obtain the particular type of tubing as aforenoted. Therefore, for tubing of the first embodiment of FIG. 1, the strip is patterned on at least one of its major surfaces and for tubing of the second embodiment of FIG. 2, the tubing is also patterned on at least one of its major faces.

Any well known patterning method could be employed to obtain the desired enhancement pattern. The method may be mechanical such as machining, or chemical such as etching. It may include masking if desired. It may be done by abrasion such as sand blasting. However, it is preferred in accordance with this invention to provide a process wherein the enhancement pattern is embossed in the strip surface and, most preferably, the embossment is provided by a process of roll embossing.

The process is applicable to a wide range of metals including steels stainless steels, aluminum and aluminum base alloys, copper and copper base alloys; how ever, it is preferably applied to copper and copper base alloys.

After the strip has been patterned, it is formed into the shape of a tube by well known tube forming techniques. Generally this comprises forming the strip gradually into the shape of a tube by passing it through a series of roll forming stands or dies. After the strip has been formed into the shape of a tube the longitudinally extending edges of the strip are joined together by conventional means, preferably, by welding and, most preferably, by high frequency welding.

The tubing thus formed may be subjected as desired to shaping and/or sizing by conventional means and any other further processing as, for example, cleaning, coiling and/or packaging.

The apparatus for practicing the process in accordance with this invention and for forming the tubing in accordance with this invention is shown schematically in FIG. 3. The apparatus comprises supply means 30 or a supply of metal strip; patterning means 40 for forming at least one heat exchange enhancement pattern on at least one surface of the metal strip; tube forming means 60 for forming the metal strip into the shape of a tube; and joining means for joining the longitudinally extending edges of the strip to form the complete tube.

The apparatus may also include shaping and/or sizing means as, for example, to correct out of roundness and properly sizethe joined tube. It may also include means for further processing 90'the tubing as, for example, means for cleaning the tube, and means for coiling the tubing. v

The particular apparatus for carrying out each of these functions may be of any conventional well known design. The supply means 30 generally comprises a supply of metal strip in the form of a coil. The tube forming means 60 generally comprises a plurality of in line tube forming roll stands or dies as are well known in the art.

The joining means 70 in accordance with this invention preferably comprises though it is not limited to a high frequency forge welding station as set forth in US. Pat. No. 3,037,105, granted May 29, 1962. The shaping and/or sizing means 80 generally comprises a series of in line roll or die stands.

The cleaning means 90 may be the one set forth in US. Ser. No. 167,687, filed July 30, 1971. The coiling means 90 may be any conventional means for coiling tubing.

The strip patterning means 40 is preferably in accordance with this invention a roll emmbossing apparatus 41 as shown in FIG. 4. t I

FIG. 4A- shows rolls 42 for embossing metal strip 43 wherein one operative roll surface 44 contains the longitudinally extending rib pattern 3 and the opposing operative roll surface 45 contains the diamond pattern 2. It is significant as aforenoted that neither of the heat exchange enhancement patterns 2 or 3 which either 'roll embosses extends throughout the thickness of the strip 43, therebypermitting the enhancement pattern 3 on one side 46 of the strip to be different from the enhancement pattern 2 on the other side 47 of the strip.

FIG. 4B shows a somewhat similar roll configuration which embosses both sides 46 and 47 of the strip 43 so it is patterned with the diamond pattern 2. From FIGS. 4A and 4B it can be readily seen that the particular enhancement patterns E on each side of the strip 43 are strictly a function of the embossing roll 42 which is employed and, therefore, are readily changeable by changing embossing rolls. 7 I

In welding strip 43 into tubing, it is necessary to accurately align the strip edges 48 after the strip has been formed, into the tube prior to welding. When an enhancement pattern E such as the diamond pattern 2 in FIG. 4B is employed, the degree'of discontinuity on the surfaces 46 and 47 of the strip 43 is not sufficient to interfere with the normal welding process. When a rib pattern 3 or other type of pattern E which provides a marked discontinuity in the strip 43 surfaces 46 and 47 is employed, it is necessary to leave longitudinally extending edge portions 49 of the strip 43 unpatterned in order to obtain accurate alignment of the strip edges 48 at the weld point.

. Referrring to FIG. 5, it is shown why it is necessary to provide these unpatterned edge portions 49 in order to maintain the alignment of the strip edges. FIG. 5 is a cross section of the tube 1 and weld rolls 50 at the point where the strip edges 48 are welded together. It is seen therein that the weld rolls 50 maintain the alignment of the strip edges 48 by contacting the strip surfaces 46 or 47 adjacent to the strip edges 48. When the strip edge portions 49 are left unpatterned, the contact between the strip surface 47 and the weld rolls 50 is the same on both sides of the weld seam 6 so that accurate alignment is maintained.

If this were not the case and, for example, the longitudinal rib pattern 3 extended across the full width of the strip 43, the strip surface at 51 contacting the weld roll on one side of the weld seam 6 could be at a valley in the rib pattern 3 whereas the strip surface at 52 contactingthe weld roll 50 on the opposing side of the weld seam- 6 could be at a peak, therefore, providing a substantial misalignment of the strip edges 48 during welding. Such a problem is completely overcome in accordance with this invention by leaving longitudinally extending edge portions 49 of the strip 43 unembossed.

Referring again to FIG. 4, it is seen that the heatexchange enhancement pattern E is readily changeable merely by changing embossing rolls 42. Therefore, in accordance with this invention, it is possible to incorporate in the apparatus as shown in FIG. 6 a plurality of embossing roll stands 100. Three are shown, how-. ever, any desired number could be employed to obtain any desired enhancement pattern E or combination of patterns in the strip surfaces 46 and 47.

Each of the roll stands shown is actuated by a pneumatic cylinder 101 which is capable of forcing it into embossing contact with the strip or removing it from contact with the s'trip. In FIG. 6, the first roll stand is shown in embossing contact with the strip. If it were desired to form the tubing of FIG. 1, a single roll stand would be sufficient although if it were desired to switch during continuous tube welding between the embodiments of FIGS. 1A through 1C, the plurality of roll stands shown would provide an easy approach.

For example, the first roll stand 102 could have a diamond pattern 2 bottom embossing roll 103 and a smooth top roll S to form thetubingl of FIG. 1A. The second roll stand 104 could have a rib pattern 3 in the top roll 105 and a diamond pattern 2in the bottom roll 103 to form the tubing 1 of FIG. 1B and the third roll stand 106 couldhave a diamond pattern 2 in the top roll 1 03 and a rib pattern 3 in the bottom roll 105, thereby being capable of forming the tubing 1 of FIG. 1C.

Therefore, by employing three roll stands as shown in FIG. 6, one could readily change from the manufacture of the tubing 1 of FIG. 1A to tubing of FIGS. 18

and 1C by merely actuating the appropriate roll stand so the embossing roll 103 or 105 contacts the strip.

The roll stands 100 of FIG. 6 are also suited for forming tubing in accordance with FIG. 2 and the like. The pneumatic cylinders 101 of each of the roll stands 100 would have to be controlled by a suitable sequencing mechanism 110 as are known in the art. When it is desired to change from one enhancement pattern E to another in the longitudinal direction of the strip 43, this sequencing could include solenoid type valves 111 in the fluid lines to the pneumatic cylinders I01 and these solenoid valves l ll could then be actuated by some conventional type switching means 110 such as a computer, cam actuated switches, electric timer or other similar means.

In operation then, for example, the first roll stand 102 could be actuated to contact the strip 43 and emboss it during a first time period to form a diamond pattern 2. During a second time period, all of the roll stands 100 could be out of contact with the strip, thereby leaving a smooth surface or perhaps the second roll stand 104 having a rib pattern 3 could be actuated. By appropriately sequencing the actuation of the respective roll stands 100, any desired pattern could be obtained as shown in FIGS. 28, 2C, 2E and 2F and any of the variations which would be readily thought of from these Figures.

To obtain patterns varying in degree of intensity as in FIGS. 2A and 2D, one could employ a further solenoid valve 120 controlled by the sequencing mechanism 110 following the solenoid valve 111 which would act to bleed the system and gradually reduce the forceexerted by the pneumatic actuator on the rolls S, 103 or 105 and, thereby, gradually reduce the depth of the enhancement pattern E in the strip 43. In such a sequence then, the solenoid valve 111 would be opened to place a roll S, 103 or 105 into embossing contact with the strip followed by opening of the bleed valve 120 to gradually withdraw the roll from embossing contact with the strip, thereby yielding the pattern varying in degree as in FIGS. 2A and 2D.

- The roll stands of FIG. 6 are situated in line in the welding apparatus and provide a marked improvement in flexibility as compared to an off line patterning system since it is possible to readily change from one heat exchange enhancement pattern to another or to change the degree of enhancement of any given enhancement pattern. This is readilyaccomplished in line by appropriately sequencing the actuation of the roll stands 100.

While the means for actuating the roll stands and the sequencing means have been described with respect to a specific embodiment,-any desired sequencing means as are well known in the art and any desired means for actuating the roll stands as are known in the art could be employed. For example, in place of the pneumatic cylinder for actuating the roll stands, hydraulic means, mechanical means or a combination of these could be employed.

The above description assumes that the strip is traveling in the direction of the arrow 200.

While the tubing shown in FIGS. 1 and 2 is enhanced throughout the complete length-of the tubes, the tubing has been shown that way for purposes of example only and portions of the outside surface of the tube may be left smooth for connection to heat exchanger plates or for other known purposes in accordance with well known practices in the art. This particularly applies to the ends of the tube.

The tubing inaccordance with this invention when joined by high frequency forge welding generally contains a weld bead on the outside and inside surfaces of the tube. Theseweld beads may be removed by well known scarfing techniques which can result in a narrow longitudinally extending region which has been scarfed and wherein the enhancement pattern has been removed. Sometimes the weld bead is insignificant and need not be removed. If a joining process other than forge welding is employed, there may be no weld bead. Therefore, this invention includes tubes which have inside and/or outside weld beads or have had them removed, or have essentially no weld beads at all.

In accordance with this invention, the heat exchange enhancement patterns do not extend throughout the full wall thickness of the tube. Therefore, the heat exchange enhancement pattern on the outside or inside surface ofthe tube does not show through on the opposing surface of the tube. This is meant to distinguish the tubing in accordance with the instant invention from corrugated tube such as shown in U.S. Pat. No. 3,2l7,799, granted Nov. 16, I965, or fluted type tubing 10 such as in U.S. Pat. No. 3,244,601, granted Apr. 5, 1966.

In the case of the corrugated or fluted tube, the enhancement patterns do extend through the full wall thickness in the sense of this invention since the corrugations or flutes on one surface of the tube form corresponding corrugations or flutes on the opposing surface of the tube.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein. What is claimed is:

1. An apparatus for forming a heat exchanger tube comprising:

embossing means communicating in line with a supply of metal strip for embossing at least one heat exchange enhancement pattern on at least one major surface of said metal strip, said pattern extending throughout only a portion of the strip thickness;

actuating means for actuating said embossing means to bring it into and out of embossing contact with said strip;

sequencing means communicating with said actuating means for appropriately sequencing the actuation of the embossing means;

tube forming means communicating in line with said patterned metal strip for forming said strip into the shape of a tube having longitudinally extending strip edges; and

joining means communicating in line with said longitudinally extending strip edges for joining them together to form the tube.

2. An apparatus according to claim 1 wherein said joining means comprises means for high frequency welding said strip edges together. 3. An apparatus accordingto claim 1 wherein said embossing means comprises at least one roll embossing stand situated intermediate said supply of metal strip and said joining means.

4. An apparatus according to claim 3 wherein said embossing means comprises a plurality of roll embossing stands.

5. An apparatus according to claim 4 wherein each of said roll embossing stands comprises a pair of rolls and said actuating means actuates at least one of said rolls in a stand to bring it into and out of embossing contact with said strip.

6. An apparatus asin claim 5 wherein said sequencing means communicates with said actuating means for appropriately sequencing the actuation of the respective roll stands during patteming so as to form heat exchange enhancement patterns which contain longitudinally extending variations in the type of enhancement.

7. An apparatus as in claim 5 wherein said sequencing means communicates with said actuating means for appropriately sequencing the actuation of the respective roll stands during patterning so as to form heat exchange enhancement patterns which contain longitudinally extending variations in the degree of enhancement.

acterized by said first pattern being on the outside of the tube and saidsecond pattern being on the inside of the tube. 

1. An apparatus for forming a heat exchanger tube comprising: embossing means communicating in line with a supply of metal strip for embossing at least one heat exchange enhancement pattern on at least one major surface of said metal strip, said pattern extending throughout only a portion of the strip thickness; actuating means for actuating said embossing means to bring it into and out of embossing contact with said strip; sequencing means communicating with said actuating means for appropriately sequencing the actuation of the embossing means; tube forming means communicating in line with said patterned metal strip for forming said strip into the shape of a tube having longitudinally extending strip edges; and joining means communicating in line with said longitudinally extending strip edges for joining them together to form the tube.
 2. An apparatus according to claim 1 wherein said joining means comprises means for high frequency welding said strip edges together.
 3. An apparatus according to claim 1 wherein said embossing means comprises at least one roll embossing stand situated intermediate said supply of metal strip and said joining means.
 4. An apparatus according to claim 3 wherein said embossing means comprises a plurality of roll embossing stands.
 5. An apparatus according to claim 4 wherein each of said roll embossing stands comprises a pair of rolls and said actuating means actuates at least one of said rolls in a stand to bring it into and out of embossing contact with said strip.
 6. An apparatus as in claim 5 wherein said sequencing means communicates with said actuating means for appropriately sequencing the actuation of the respective roll stands during patterning so as to form heat exchange enhancement patterns which contain longitudinally extending variations in the type of enhancement.
 7. An apparatus as in claim 5 wherein said sequencing means communicates with said actuating means for appropriately sequencing the actuation of the respective roll stands during patterning so as to form heat exchange enhancement patterns which contain longitudinally extending variations in the degree of enhancement.
 8. An apparatus as in claim 1 wherein said embossing means embosses a first heat exchange enhancement pattern on one side of said metal strip and a second heat exchange enhancement pattern on the opposite side of said metal strip so that the resultant tube is characterized by said first pattern being on the outside of the tube and said second pattern being on the inside of the tube. 